Abstract:
Tests of sub-photospheric stellar structure and evolution are few
and far between. In addition to asteroseismology, color-magnitude
diagram (CMD) morphology, and abundance anomalies among evolved stars,
an increasingly valuable probe of stellar structure for lower mass main
sequence and post-main sequence stars is the Li abundance. Building
upon our recent work in NGC 3680 and NGC 6253, we propose to derive
A(Li) for every probable member single star in NGC 2420 from the tip of
the giant branch to 2.5 mag below the turnoff. NGC 2420 is one of very
few metal-deficient open clusters with stars within observational reach
on both sides of the Li-dip. The observations will allow mapping of
convection along the giant branch for stars near the He-degenerate core
boundary, better definition of the metallicity dependence of the Li-dip,
and constraints on any depletion of Li among the cooler stars that
populate the analogous Spite plateau within the halo.